Gold nanoparticles display unique optical properties. These properties make gold nanoparticles useful tools for biotechnology and medicine. Gold nanoparticles are also called nano gold or colloidal gold due to the fact that they are less than 100nm in size and are suspended in a liquid solution. The color of the colloidal gold is dependent upon the size and shape of the gold nanoparticles comprising it. Larger particles and aggregates of particles cause the absorbance spectrum to broaden and shift towards longer wavelengths and a red color. The metallic nature of the particles makes them very useful for imaging by electron microscopy, which was one of the first applications for them. The gold nanoparticles can be functionalized with antibodies, carbohydrates, and nucleic acids. This makes them very useful for scanning electron microscopy (SEM), transmission electron microscopy (TEM), and confocal light microscopy as well as pathogen detection and other diagnostic assays. The ability of gold to absorb light via surface plasmon resonance (SPR) makes them useful tools for photothermal therapy in the treatment of cancer.
The ELISA, or enzyme linked immunosorbent assay, is the gold standard immunoassay for detection of small quantities of protein in samples as varied as serum, urine, saliva, and more. The ELISA is a labeled assay, which means that some type of label is needed to detect protein binding events. These labels are typically fluorescent, chromatic, or chemiluminiscent, and require the use of a plate reader to quantify the amount of protein in the sample. The major benefit of the ELISA is that low concentrations (often down to pg/mL) of protein are easily quantified. One disadvantage to ELISA is that many steps and reagents are required throughout the protocol. However, this can be mitigated by purchasing an ELISA kit that is pre-bound with capture antibodies and contains a detailed protocol for using all of the included buffers in a clear, easy to follow format. The use of an ELISA kit can improve diagnostic results from assay to assay because the kits are all validated between lots and come with protein standards. This means that a standard curve (detected signal vs. protein concentration) is generated during each assay and this standard curve can be checked against the expected values to ensure that the kit is still functioning as expected. The kit streamlines the process and takes the guesswork out of protocol design.
Antibodies are produced by the adaptive immune system in response to invading pathogens. The antibody has specific lock and key recognition for the offending bacteria, virus, or other molecule, which are collectively called antigens. Antibodies are proteins, which are folded polypeptides, or strands of amino acids which have antigen recognition sites that specifically recognize a binding site of its specific antigen. They are produced by B-cells of the adaptive immune system.
As with any nanoparticle, the properties of silver nanoparticles are dependent on size. Many synthesis strategies produce nanoparticles with a wide size distribution. One way to separate these particles based on size is to use density gradient centrifugation. A sucrose gradient is an easy way to perform this separation because the sucrose gradient is simple to create using common laboratory equipment.
Proteins are fundamental building blocks for life. All tissues and organisms are made up of protein, and all of the work performed inside and outside of cells is mediated by protein signaling cascades. Proteins are polymers of amino acids with three or four layers of organized structure. Primary structure is defined as the linear order of amino acids. This is dictated by the genome: the code is transcribed from DNA and translated into the string of amino acids. Secondary structure is thought of as two basic forms: a beta sheet or alpha helix. The string of amino acids adopts the conformation that allows the lowest energy state. Beyond the sheets and helices, the chain can take other twists and turns to fold into a shape known as its tertiary structure. Some proteins are actually made up of two or more subunits of individually folded amino acids strands. The complexing of protein subunits to form one functional protein is called quaternary structure. All of this folding is extremely important to the character and function of each individual protein because it results in certain side chains of amino acids being located on the exterior or interior of the protein. Importantly, the folds create binding pockets where key amino acids are located to create a unique chemical landscape that allows the protein to bind to other proteins and carry out its job in a signaling cascade.
An in vitro diagnostic product (IVD) is any reagent, device, system, or part of a system used outside of the body to diagnose a disease or infection. The IVD can be used to detect DNA/RNA, microorganisms, or protein. This can be in a laboratory setting or in a “point of care setting.” Point of care (POC) is beneficial because it removes the need to send a sample to a laboratory for testing. Therefore, the time between sample collection and diagnosis is significantly reduced. Point of care IVD is especially useful in resource-poor settings where laboratories are located far away and there is a lack of good communication or transportation infrastructure.
Gold has always held a special allure for humans throughout history: wars were fought over it, alchemists strived to turn other metals into it, graves were looted for it, and love was sworn by it. Gold is so entwined in our lives that many people don’t even realize that it is fundamental to many state-of-the-art biotechnology. One of the most useful modern properties of gold is the creation of a surface plasmon resonance condition upon exposure to incident light of a resonance frequency. Gold used in this way is applied as a thin layer on a surface plasmon resonance (SPR) chip or is used as nanoparticles in Surface Enhanced Raman Scattering (SERS). These aqueous solutions of gold nanoparticles (5-50 nm in diameter) are the least recognizable form of gold because these colloidal solutions actually appear reddish in color rather than the characteristic yellow color of larger solid gold. It turns out that the work of the alchemists was not wasted. The discovery of aqua regia (noble or royal water) by an alchemist in the 8th century AD is critical to gold nanoparticle synthesis. This powerful mixture of nitric acid and hydrochloric acid is capable of dissolving solid gold to make chloroauric acid, which is the starting point for gold nanoparticle synthesis.
Cell separation is widely used in research and clinical therapy. For research purposes, sorting cells from a heterogeneous population enables the study of the different isolated types. From a therapeutic perspective, cell separation allows for the therapeutic infusion of enriched cell populations into a patient. Moreover, the latest advances in stem cell therapy, tissue engineering and regenerative medicine show the potential of cells derived from different tissues. The use of highly selective separation processes is critical to improve the quality of these cell-based treatments.